1. Field of the Invention
The present invention relates to an exposure method and apparatus for accurately exposing a sensitized substrate with a pattern formed on a mask through a projection optical system, and is particularly preferable for a scan-exposure method used in a lithography process for manufacturing a circuit device such as a semiconductor circuit element, a liquid crystal display element, etc.
2. Description of the Related Art
Currently, on a semiconductor device manufacturing scene, a step-and-scan projection exposure apparatus which scan-exposes the whole of a circuit pattern of a reticle to one shot area on a wafer, by using an ultraviolet pulse laser beam having a wavelength of 248 nm from a KrF excimer laser light source or an ultraviolet pulse laser beam having a wavelength of 193 nm from an ArF excimer laser light source as an illumination light, and by performing one-dimensional scanning for a reticle (original version, mask substrate) and a semiconductor wafer, on which a circuit pattern is drawn relatively to a projection field of a reduction projection lens system, is a promising exposure apparatus for manufacturing a circuit device.
Such a step-and-scan projection exposure apparatus has been commercialized and marketed as a micra-scan exposure apparatus which is equipped with a reduction projection optical system composed of a dioptric element (lens element) and a catoptric element (concave mirror, etc.), and is provided by Perkin Elmer Corporation. As explained in detail, for example, on pp. 424-433 in Vol. 1088 of SPIE in 1989, the micra-scan exposure apparatus exposes a shot area on a wafer by scanning and moving a reticle and the wafer at a speed rate according to a projection magnification (reduced to one-fourth) while projecting part of the pattern of the reticle onto the wafer through an effective projection area restricted to an arc slit shape.
Additionally, as a step-and-scan projection exposure method, a method combined with the method which uses an excimer laser light as an illumination light, restricts to a polygon (hexagon) the effective projection area of a reduced projection lens system having a circular projection field, and makes both ends of the effective projection area in a non-scanning direction partially overlap, what is called, a scan-and-stitching method is known, for example, by the Japanese laid-open Publication No. 2-229423 (Jain). Additionally, examples of a projection exposure apparatus adopting such a scan-exposure method are disclosed also by the Japanese laid-open Publications No. 4-196513 (NC:Nishi), No. 4-277612 (NC:Nishi), No. 4-277612 (NC:Nishi), No. 4-307720 (NC:Ota), etc.
With the apparatus which restricts an effective projection area of a projection optical system to an arc or a rectilinear slit shape among projection exposure apparatuses of a scan-exposure type, an image distortion of a pattern transferred onto a wafer as a result of scan-exposure depends on each aberration type of the projection optical system itself or an illumination condition of an illumination optical system as a matter of course. Such an image distortion became an important error budget also for a stepper of a method (stationary exposure method) with which a circuit pattern image on a reticle, which is included in a projection field, is collectively transferred in a shot area on a wafer in a state where a mask and the wafer are made stationary.
Accordingly, a projection optical system mounted in a conventional stepper is optically designed so that the image distortion vector (the direction and the amount of the deviation from the ideal position of each point image at an ideal lattice point), which occurs in each lattice point image, becomes averagely small in an entire projection field. Lens elements and optical members are processed with high accuracy, and assembled as the projection optical system by repeating complicated and time-consuming tests in order to include the image distortion vector within a tolerable range when being designed.
To ease, however little, the difficulty in the manufacturing of such a projection optical system, which requires high accuracy, the method for actually measuring the image distortion characteristic of an assembled projection optical system, for inserting the optical correction plate (quartz plate), which is polished to partially deflect the principal ray passing through each point in a projection field, in a projection optical path so that the actually image distortion characteristic becomes a minimum at each point in the projection field is disclosed, for example, by the Japanese Unexamined Patent Publication No. 8-203805 (NC).
Additionally, the Japanese laid-open Publication No. 6-349702 (Nikon) discloses the method for adjusting aberration characteristics of a projection optical system by rotating some of lens elements configuring the projection optical system about an optical axis in order to improve the image distortion characteristic occurring in a resist image on a photosensitized substrate, which is transferred by scan-exposure. Furthermore, as disclosed by the Japanese laid-open Publications No. 4-127514 (NC:Taniguchi) and No. 4-134813 (N:shiraishi), it is also known that a projection magnification, a distortion aberration, etc. are adjusted by infinitesimally moving some of lens elements configuring a projection optical system.
However, there is a problem in that even if an aberration characteristic is adjusted by rotating some of lens elements configuring a projection optical system or by decentering or tilting an optical axis, this does not always guarantee that a satisfactory aberration characteristic (image distortion characteristic) can be obtained. Furthermore, it is difficult to partially adjust and modify respective characteristics such as a local image distortion, etc. within a projection area.
Therefore, if the optical correction plate disclosed by the Japanese Unexamined Patent Publication No. 8-203805 (NC:Nikon) is manufactured and inserted in a projection optical path, it is anticipated that a local image distortion characteristic within an effective projection area can be easily improved. However, the conventional optical correction plate explained in the Japanese Unexamined Patent Publication No. 8-203805 (NC:Nikon) is not assumed to be applied to the projection optical system used for scan-exposure. Accordingly, if an optical correction plate is manufactured with the method disclosed in this publication as it is, its design and manufacturing become extremely complicated. Especially, the accuracy for processing the shape of a local surface of the optical correction plate with a wavelength order (order of nanometer to micrometer) becomes stricter.
The present invention was developed in the above described background. A first object of the present invention is to provide an exposure method and apparatus which can accurately expose a substrate with a pattern formed on a mask.
A second object of the present invention is to provide an exposure method and apparatus which can form a mask pattern image on a substrate in a desired state.
A third object of the present invention is to provide an exposure method and apparatus which comprises an optical correction element suitable for a scan-exposure method, and can easily reduce a projection aberration occurring at the time of scan-exposure.
A further object of the present invention is to provide an exposure method for easily reducing an image distortion error occurring when being scan-exposed by using the projection optical system including optical correction elements suitable for a scan-exposure method.
A still further object of the present invention is to provide a projection exposure apparatus including such optical correction elements, and the method for manufacturing a circuit device by using the projection exposure apparatus.
A still further object of the present invention is to provide an image formation performance automatic measurement system for use in a lithography device, which measures an image distortion error of a projection optical system including an optical correction element yet to be processed in a state of being mounted in a projection exposure apparatus of a scanning type, and can automatically simulate a process condition such as a plane shape of an optical correction element to be processed and an installment condition (tilt, etc.) for the projection optical system based on the result of the measurement.
A still further object of the present invention is to easily self-test the performance of a projection exposure apparatus periodically or depending on need by using such an image formation performance automatic measurement system.
A still further object of the present invention is to immediately obtain a change in an image formation performance, which can possibly occur while a projection exposure apparatus is being used on a manufacturing line, especially, a change in a random image distortion error (aberration characteristic).
According to one aspect of the present invention, a pattern of a mask (R) is scan-exposed onto a substrate (W) by moving the mask(R) and the substrate (W) in a scanning direction in a state where the mask (reticle R) is arranged on an object plane side of a projection optical system (PL) having a predetermined image formation characteristic, the substrate (wafer W) is arranged on its image plane side, a partial image of the mask (R) which is projected onto the image plane side is restricted to within a projection area (EIA) having a predetermined width in a one-dimensional scanning direction, and at least one optical correction element (an image distortion correction plate G1, an astigmatism/coma correction plate G3, or an image plane curvature correction plate G4), which is optically processed so that an average aberration characteristic obtained by averaging the projection aberrations at a plurality of image points existing in sequence in the scanning direction becomes a predetermined state at each of a plurality of positions in a non-scanning direction intersecting the scanning direction of the projection area (EIA), is arranged in an image formation optical path by a projection optical system (PL).
According to the present invention of the above described configuration, it becomes possible to satisfactorily correct projection aberrations influenced by the aberrations of both of an illumination optical system and a projection optical system, especially, a dynamic distortion characteristic, an astigmatism characteristic, a coma characteristic, and an image plane curvature characteristic at the time of scan-exposure, thereby accurately exposing a mask pattern onto a substrate.
According to another aspect of the present invention, in an exposure method for exposing a substrate (W) by projecting a pattern of a mask (R) onto the substrate (W) through a projection optical system (PL), a mask pattern image is projected through the projection optical system in a state where the mask (R) and the substrate (W) are arranged, and an astigmatism correction plate (G3) for correcting a random astigmatism characteristic of each image at a plurality of positions within a projection area (EIA) of the projection optical system is arranged between the mask (R) and the substrate (W) in order to expose the substrate.
According to the present invention, it becomes possible to satisfactorily correct a random astigmatism characteristic within a projection area, thereby accurately exposing a mask pattern onto a substrate.
According to a further aspect of the present invention, in an exposure method for exposing a substrate (W) by projecting a pattern of a mask (R) onto the substrate (W) through a projection optical system (PL), a mask pattern image is projected through a projection optical system in a state where the mask (R) and the substrate (W) are arranged, and a coma correction plate (G3) for correcting a random coma characteristic of each image at a plurality of positions within a projection area (EIA) of the projection optical system (PL) is arranged between the mask (R) and the substrate (W) in order to expose the substrate.
According to the present invention, it becomes possible to satisfactorily correct a random coma characteristic within a projection area, thereby accurately exposing a mask pattern onto a substrate.